1. Field of the Invention
The present invention relates to optical disk writing apparatuses, and particularly, to an optical disk writing apparatus that can control output.
2. Description of the Related Art
“Write Pause” refers to a standby status of output during a recording operation of an optical pickup. In a conventional optical pickup, the level of output is modified to the output obtained by OPC (Optical Power Control) when output is to be adapted to a writing state. It cannot be said that the output of the optical pickup in such a case is optimum. Accordingly, there is developed a method to correct the output of the optical pickup concurrently with the actual recording operation (running OPC).
Running OPC is disadvantageous in that it is difficult to correct the output properly when the period of time of emission of a laser beam is short since control becomes complex. In view of such a problem, various methods of controlling the output of a pickup properly in a simple manner have been proposed.
The running OPC disclosed in Japanese Patent Laying-Open No. 2001-312822 includes the steps of irradiating an optical disk with at least two laser beams, i.e. a first laser beam having an intensity that can form a pit on the recording plane of the optical disk and a second laser beam having an intensity lower than the lowest intensity required to form a pit and higher than the lowest intensity required for reproduction, forming a pit corresponding to a recording signal on the optical disk using the first laser beam as well as reading out an RF (Radio Frequency) signal of the pit formed by the first laser beam, using the second laser beam, and correcting the recording power of the first laser beam based on an asymmetry value of the RF signal read out by the second laser beam.
This method allows measurement of an accurate asymmetry value through simple control to conduct running OPC of high precision.
Japanese Patent Laying-Open No. 2004-110993 discloses a method of selecting laser power required to record a modulation code onto an information recording medium using a laser. This method includes the steps of recording a predetermined signal pattern on an information recording medium, reproducing the recorded predetermined signal pattern and calculating an asymmetry value from the reproduced predetermined signal pattern, obtaining the rate of change of the laser power of the asymmetry value, and selecting the laser power corresponding to the highest rate of change.
In accordance with this method, a recording power can be selected based on the asymmetry value even for a recording medium that conventionally could not use an asymmetry value.
The optical disk recording method disclosed in Japanese Patent Laying-Open No. 2002-352426 includes the steps of modulating the optical beam to have a recording power corresponding to recording and another power corresponding to the case where recording is not conducted, and irradiating the track of the optical disk, according to the recording signal, with the appropriate power to record a recording signal, wherein detection is made of the component of periodic fluctuation in the output of the optical beam that occurs repeatedly according to the disk orbit, and correcting the optical beam output in a recording power mode so as to cancel the periodic fluctuation component.
In accordance with this method, recording of high quality can be carried out even if wobbling or eccentricity occurs at the optical disk. Further, an appropriate recording power can be detected at high accuracy even if the optical disk exhibits wobbling or eccentricity.
The approach of irradiating an optical disk with at least two laser beams, and correcting the recording power of the first laser beam based on the asymmetry value of an RF signal read out by the second laser beam, as disclosed in Japanese Patent Laying-Open No. 2001-312822, is disadvantageous in that control becomes complex. This is due to the fact that control of each of the plurality of laser beams is required. Since tracking is generally required, an optical pickup apparatus must control a plurality of laser beams. Such laser beams are primary emitted for the purpose of tracking. Therefore, the control will become complex when the intensity of the laser beam is to be controlled for recording based on a plurality of laser beams. Even if a technique is developed to render the laser beam for tracking dispensable in the future, the need to control a plurality of laser beams will still arise.
The method disclosed in Japanese Patent Laying-Open No. 2004-110993 obtains the output through the OPC set forth above. Therefore, there is a problem that the output of the optical pickup is not optimum.
When the periodic fluctuation component of an optical beam output is detected and the optical beam output in a recording power mode is to be corrected so as to cancel the detected periodic fluctuation component, as disclosed in Japanese Patent Laying-Open No. 2002-352426, the periodic fluctuation of output is just suppressed taking advantage of reflected light. Such an approach involves the problem that optimization of the laser output is still required to be further improved.